Assessing the Accuracy of Vertical Profiles of Heating and Vertical Motion in the Tropical Eastern Pacific

Abstract

Vertical profiles of heating (Q1) are a result of the interaction between radiative heating, eddy sensible heat transport, and latent heating from cloud and precipitation systems. The third component is the largest by an order of magnitude in deep convective regions like the intertropical convergence zone (ITCZ). Vertical motion (ω) is often used as a proxy for Q1 and, in regions lacking in situ observations, ω profiles from model reanalyses are commonly used to make inferences about large-scale circulations and climate sensitivity. In the East Pacific (EP) ITCZ, ω profiles exhibit large variability between reanalyses and have a bottom-heavy shape centered near 800 hPa that contrasts with the 400 hPa peak in the West Pacific (WP) warm pool. Rainfall between the two regions is similar; however, stratiform rain fractions are higher in the EP than the WP, and the low-level ω peak in the profiles persists even during El Niño, when precipitation systems become similar between the two regions. These facts all point towards erroneous reanalysis profiles in the EP.

Echo statistics from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and the Dual-frequency Precipitation Radar (DPR) aboard the Global Precipitation Measurement (GPM) satellite are examined across the tropical Pacific. The DPR Ku-band is more sensitive to upper level, low-reflectivity cloud and sees more near-surface echo than the PR, but the overall echo statistics are generally similar. The addition of the DPR Ka-band high sensitivity scans further enhances the DPR sensitivity to upper level cloud, but echo statistics are still not substantially different than TRMM. Utilizing the 16-year TRMM climatology for increased sampling, previously known differences in convection between the EP and WP are confirmed, but they aren’t great enough to justify such a large discrepancy in reanalysis ω profiles.

The relationships between Q1 and ω to rainfall statistics in select tropical field campaigns are also investigated. In all cases, the magnitude and height of the peak values of each variable increase with increasing stratiform rain fraction, further suggesting that the EP should have top-heavy rather than bottom-heavy heating and ω because of its higher stratiform rain fraction.